1. Field of the Invention
The present invention relates generally to a method and an apparatus for input on a touch screen, and more particularly, to a method and an apparatus for input on a capacitive-type touch screen.
2. Description of the Related Art
Referring initially to FIG. 1, a diagram illustrates a side-sectional view of a mutual touch screen panel. The mutual touch screen panel includes a first electrode layer 11 in a lower section thereof, and a second electrode layer 13 spaced apart from the first electrode layer 11 by a predetermined distance. The first electrode layer 11 and the second electrode layer 13 are separated by a substrate 15 having a predetermined dielectric constant. The first electrode layer 11 and the second electrode layer 13 include a plurality of electrode lines. The electrode lines of the first electrode layer 11 and the electrode lines of the second electrode layer 13 cross. An upper portion of the touch screen panel further includes a tempered glass 17 for protecting the second electrode layer 13.
The first electrode layer 11 is connected to a first circuit for applying a predetermined signal. When the predetermined signal is applied to the first electrode layer 11 from the first circuit, an electric field is generated between the first electrode layer 11 and the second electrode layer 13. The predetermined signal applied to the first electrode layer 11 is transferred to the second electrode layer 13 through the electric field. The signal transferred to the second electrode layer 13 is supplied to a second circuit. The second circuit determines a change in the signal transferred from the second electrode layer 13, identifies whether a touch is input, and identifies coordinates of an area in which the touch is input. Specifically, referring to FIG. 2, when a touch by a user 19 or a stylus pen is not input, the signal transferred from the second electrode layer 13 is in the form of a reference signal 21. However, when a touch by the user 19 or the stylus pen is input, a change of a contact strength detected in the second electrode layer 13 represents a pattern of a contact strength signal 22. Further, a change of a quantity of the electric field transferred from the second electrode layer 13 in the area in which the touch by the user 19 or the stylus pen is input is in the form of an output signal 23. Specifically, the output signal 23 has a form indicating a relatively lower value than a predetermined level in a section 24 in which the touch is input, because the quantity of the electric field coupled to the second electrode layer 13 from the first electrode layer 11 is decreased by the contact with the user.
The second circuit identifies the contact strength signal 22 to determine whether the touch is input, and identifies coordinates of the area in which the touch is input.
The mutual touch screen panel senses the change in capacitance by the contacted conductor. Accordingly, as the change in capacitance increases, there is a greater likelihood of operation without error. In order to increase the change in capacitance, it is preferable to increase a contact area. The touch screen device has a sensing performance that is sufficient to detect a change in capacitance corresponding to a contact of a finger. The change in capacitance by the contact of the finger is a very small quantity of several picoFarads (pF). Accordingly, a great deal of effort is required to decrease noise influence in the processing of signal detection.
Although the touch screen device operates at a satisfactory level in a user interface by a finger, the sensitivity of the touch screen device must be improved to detect an input in an approach process or to perform an operation by a contact of a conductive pen having a contact area smaller than that of the finger. The improvement in sensitivity means a decrease in a threshold level, such that the touch screen device responds to a smaller signal. However, if the threshold level is only decreased when at least a predetermined level of a signal-to-noise ratio is not secured, a probability of generating a malfunction may be increased.
A method of amplifying a size of a signal does not have a means for isolating a noise signal before the amplification. It is impossible to obtain any gain in the signal-to-noise ratio because a noise level is simultaneously amplified.